Interest in spin polarization and spin injection into electronic devices has resulted in the development of dilute magnetic semiconductor (DMS) materials. The discovery of carrier-induced ferromagnetism in DMS materials has resulted in further studies of DMS materials. Of particular interest is the potential for exploiting the ferromagnetic properties of DMS materials for use in data storage, data processing, semiconductor, and/or optoelectronic systems.
Previous efforts to develop spin polarization and spin injection of carriers in electronic devices were focused on the direct electrical injection of polarized electrons using a ferromagnetic metal/semiconductor junction. However, this approach can suffer from the scattering of the spin polarized carriers at the metal/semiconductor interface. A different approach involved the growth of magnetic semiconductor films to form DMS materials. In particular, research on DMS materials has focused on binary alloys of II–VI and III–V materials, such as BeSe, GaAs, and GaN materials.
In 1989, carrier induced ferromagnetism was discovered in (In,Mn)As. (See, H. Munekata, H. Ohno, S. von Molnar, A. Segmuller, L. L. Chang, and L. Esaki, Physical Review Letters, 63, 1849 (1989)). In 1996, carrier induced ferromagnetism was discovered in (Ga,Mn)As. (See, H. Ohno, A. Shen, F. Matsukura, A. Oiwa, A. Endo, S. Katsumoto, and Y. Iye, Applied Physics Letters, 69, 363 (1996)). The ferromagnetic properties of the disclosed materials, however, were limited to temperatures below 110 K.
Since the discovery of ferromagnetic properties in III–V material systems at low temperatures, many attempts to develop materials exhibiting ferromagnetic properties at room temperature have been made. In particular, III–V material systems involving GaAs have been developed. DMS materials exhibiting Curie temperatures on the order of 110 K have been reported for (Ga,Mn)As materials. Such films were grown using molecular beam epitaxy at low temperatures to produce the Mn-doped GaAs. (See, H. Ohno, J. Magn. Magn. Mater. 200, 110 (1999); see also, Y. Ohno, D. K. Young, B. Beschoten, F. Matsukura, H. Ohno, and D. D. Awschalom, Nature 402 (1999) 790).
Another approach involves creating spin polarization in the II–VI materials of the semiconductor BexMnyZn1-x-ySe. (See, R. Fiederling, M. Keim, G. Reuscher, W. Ossau, G. Schmidt, A. Wang and L. W. Molenkamp, Nature 402 (1999) 787). However, the proposed BexMnyZn1-x-ySe material exhibits low magnetic ordering temperatures, which can limit potential use of the material to applications below room temperature.
Numerous attempts to develop room temperature ferromagnetic properties in GaN heterostructures have been proposed. A theoretical model predicting ferromagnetic behavior of various Mn-doped semiconductors predicted that the DMS material (Ga,Mn)N would exhibit a Curie temperature above room temperature for p-type semiconductors wherein the doping includes at least 5 percent manganese. (T. Dietl, H. Ohno, F. Matsukura, J. Cibert, and D. Ferrand, Science 287, 1019 (2000)).
Several attempts have been made to develop GaN-based DMS materials exhibiting ferromagnetic properties above room temperature. Growth of (Ga,Mn)N by Molecular Beam Epitaxy has formed films with Curie temperatures on the order of 20 K. (See, S. Kuwabara, K. Ishii, S. Haned, T. Kondo, and H. Munekata, Physica E 10, 233–236 (2001)). Growth of (Ga,Mn)N films by metal-organic chemical vapor deposition (MOCVD) have produced information on the optical properties of (Ga,Mn)N films.
Previous formation of semiconductor magnetic materials of the II–VI and III–V type materials tend to have low magnetic ordering temperatures, which may limit such material systems to potential applications carried out below room temperature. Further, proposed theoretical models of ferromagnetic III–V material systems do not appear to have resulted in ferromagnetic III–V material systems exhibiting ferromagnetic properties at or above room temperature. Therefore, it is desirable to form a semiconductor magnetic material of the III–V type materials exhibiting ferromagnetic properties at or above room temperature.